US 7418336 B2 Abstract The invention comprises a method to operate a direct-injection engine operative at various air/fuel ratios. The method comprises monitoring in-cylinder pressure, along with a corresponding engine crank position to periodically to determine instantaneous in-cylinder pressure states corresponding to the engine crank position during compression and expansion. Pressure ratios are determined based upon the instantaneous in-cylinder pressure states. A combustion heat release is determined based upon the pressure ratios. An aspect of the invention comprises extending the operation to diesel, diesel premixed and to HCCI engines.
Claims(20) 1. Method to operate an internal combustion engine, said engine comprising a multi-cylinder direct-injection engine operative lean of stoichiometry; each cylinder including a variable volume combustion chamber defined by a piston reciprocating therein between top-dead-center and bottom-dead-center points and a cylinder head; the piston reciprocating in repetitive cycles each cycle comprising intake, compression, expansion, and exhaust strokes, the method comprising:
adapting a plurality of pressure sensing devices to monitor in-cylinder pressure during ongoing engine operation;
monitoring in-cylinder pressure and a corresponding engine crank position to periodically to determine instantaneous in-cylinder pressure states corresponding to the engine crank position during the compression and expansion strokes;
determining a plurality of pressure ratios based upon the instantaneous in-cylinder pressure states; and,
determining a combustion heat release based upon the plurality of pressure ratios.
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9. Method to operate an engine, said engine comprising a direct-injection, four-stroke, internal combustion engine including a variable volume combustion chamber defined by a piston reciprocating within a cylinder between top-dead-center and bottom-dead-center points and a cylinder head; the piston reciprocating in repetitive cycles each cycle comprising intake, compression, expansion, and exhaust strokes, the method comprising:
operating the engine lean of stoichiometry;
adapting a plurality of pressure sensing devices to monitor in-cylinder pressure and a corresponding engine crank position during ongoing operation;
determining a plurality of instantaneous in-cylinder pressure states corresponding to the engine crank position during the compression and expansion strokes;
determining a plurality of pressure ratios based upon the instantaneous in-cylinder pressure states; and,
determining a combustion heat release for each cycle for each cylinder based upon the plurality of pressure ratios.
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16. Method to monitor engine operation, said engine comprising a direct-injection, four-stroke, internal combustion engine including a variable volume combustion chamber defined by a piston reciprocating within a cylinder between top-dead-center and bottom-dead-center points and a cylinder head; the piston reciprocating in repetitive cycles each cycle comprising intake, compression, expansion, and exhaust strokes, the method comprising:
adapting a pressure sensing device to monitor in-cylinder pressure corresponding to engine crank position during ongoing operation;
determining instantaneous in-cylinder pressure states corresponding to the engine crank position during the compression and expansion strokes;
determining a cylinder pressure ratio at an engine crank angle based upon the instantaneous in-cylinder pressure states;
determining a combustion heat release based upon the pressure ratios;
and,
estimating a mass of fuel burned in the cylinder based upon the combustion heat release.
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Description This application claims priority from U.S. Provisional Application No. 60/794,411, filed Apr. 24, 2006, entitled ENGINE CONTROL. This invention relates to operation and control of internal combustion engines, including compression-ignition engines. The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. A variety of intrusive and non-intrusive pressure sensing means are known for sensing pressure within an internal combustion engine cylinder when the engine is motoring and when the engine is firing. Various aspects of internal combustion engine controls are known which rely on in-cylinder pressure measurements, particularly location of peak pressure (LPP), indicated mean effective pressure (IMEP) calibration and absolute peak pressure. Known pressure ratio management (PRM) methods provide timing and cylinder charge control using constant property assumptions applicable to operating ranges of conventional spark ignited engines. The methods as relate to conventional spark ignited engines are based on constant property assumptions and computations of the ratio of fired to motored pressure during each engine cycle. From this, combustion timing can be estimated along with a parameter related to cylinder charge strength. Compression-ignition engines and other engine control schemes operate over broad engine conditions, and effective control, including fuel control, fuel tailoring, charge ignition timing control, exhaust gas recirculation (EGR) control, is necessary to meet operator demands for performance and fuel economy and comply with emissions requirements. Furthermore, there is much variability, including that related to: components, e.g., fuel injectors; systems, e.g., fuel line and pressures; operating conditions, e.g., ambient pressures and temperatures; and, fuels, e.g., cetane number and alcohol content. The variability affects heat release and work output from individual cylinders, resulting in non-optimal performance of the engine. Any change in the engine performance is apparent in cylinder pressure ratios. Referring now to What is described herein comprises a method to monitor engine operation to determine engine heat release and combustion phasing, especially adapted for varying operating conditions that are related to compression ignition engines and homogeneous charge compression ignition (HCCI) engines having a wide range of cylinder charge temperatures and compositions. In accordance with an embodiment of the invention, there is provided a method and system to operate an internal combustion engine, said engine comprising a multi-cylinder direct-injection engine operative lean of stoichiometry wherein each cylinder includes a variable volume combustion chamber defined by a piston reciprocating therein between top-dead-center and bottom-dead-center points and a cylinder head. The piston reciprocates in repetitive cycles with each cycle comprising intake, compression, expansion, and exhaust strokes. The method includes adapting a plurality of pressure sensing devices to monitor in-cylinder pressure during ongoing engine operation. In-cylinder pressure is monitored along with a corresponding engine crank position to periodically to determine instantaneous in-cylinder pressure states corresponding to the engine crank position during the compression and expansion strokes. Pressure ratios are determined based upon the instantaneous in-cylinder pressure states. A combustion heat release is determined based upon the plurality of pressure ratios. The invention applies to diesel, diesel premixed and to HCCI engine operation. The invention may take physical form in certain parts and arrangement of parts, the embodiments of which are described in detail and illustrated in the accompanying drawings which form a part hereof, and wherein: The invention described herein comprises a method to ongoingly monitor operation and determine combustion parameters, including combustion phasing and heat release of a multi-cylinder internal combustion engine. The engine is adapted to operate over a broad range of temperatures, cylinder charge (air, fuel, and, EGR) and injection events. The method is particularly suited to operation with direct-injection compression-ignition engines operating lean of stoichiometry to determine parameters which correlate to heat release in each of the combustion chambers during ongoing operation. The method is further applicable to other engine configurations, including spark-ignition engines, including those adapted to use homogeneous charge compression ignition (HCCI) strategies. The method is applicable to systems utilizing multiple fuel injection events per cylinder per engine cycle, e.g., a system employing a pilot injection for fuel reforming, a main injection event for engine power, and, where applicable, a post-combustion fuel injection event for aftertreatment management, each which affects cylinder pressure. In the invention, the engine preferably comprises a direct-injection, four-stroke, internal combustion engine including a variable volume combustion chamber defined by the piston reciprocating within the cylinder between top-dead-center and bottom-dead-center points and a cylinder head comprising an intake valve and an exhaust valve. The piston reciprocates in repetitive cycles each cycle comprising intake, compression, expansion, and exhaust strokes. Pressure sensing devices, preferably low-cost sensors not requiring detailed calibration, zeroing, and trimming, are installed in the engine to monitor in-cylinder pressure in each of the cylinders during ongoing operation. Exemplary sensors are described hereinafter. In operation, in-cylinder pressures are monitored along with a corresponding engine crank position to determine instantaneous in-cylinder pressure states corresponding to the engine crank position, especially of interest during the compression and expansion strokes. Pressure ratios are calculated based upon the instantaneous in-cylinder pressure states, preferably at each measurement of cylinder pressure. The method comprises deriving a pressure-ratio management (PR) term that is property-dependent for use in engine management and control. The properties are temperature-dependent and cylinder charge-dependent. The PR term is applicable to engine control for accurate fueling estimation during multiple injections per combustion event, as it periodically determines PR throughout each combustion cycle. The PR provides an estimate of the amounts of fuel burnt during individual pilot, main and post combustion fuel injection events. Less sampling resolution is required for PR because its computation is performed for predefined crank angles, corresponding to inputs from a crank sensor. The PR term can be used to control combustion phasing for pilot injection, main combustion, and post-combustion injections. Parameters related to combustion heat release and combustion phasing are determined for each cycle for each cylinder based upon the calculated pressure ratios. The method monitors signal samples during compression and assumes a polytropic compression to generate a reference for floating pressure signal level. Polytropic compression may be expressed as follows:
For the PRM technique an ideal motoring pressure is computed through the cycle. Ideal motoring assumes that n is constant and there is no heat loss. There are two elements to determining the PR term constant volume heat addition and adiabatic polytropic expansion. Both derivations start with the first law of thermodynamics. The general form of the first law of thermodynamics for a closed system, e.g., a combustion chamber as depicted with reference to wherein dU is the internal energy change in the system (Eq. (2)); W is the work done by the gas on the piston (Eq. (3)) and Qch and Qht are the heat addition by fuel and the heat transfer out from the system, respectively (Eq. (2-3)). Crevice and blow-by flows are neglected in the current derivation.
wherein m is the total mass within the system boundary, cv is the constant volume specific heat, P is the cylinder pressure, LHV is the lower heating value of a fuel, A is the exposed combustion chamber surface area, h is the heat transfer coefficient, Tg is the mean gas temperature, Tw is the cylinder wall temperature, and qwf is the wall heat transfer fraction of fuel energy. The analytical solution for deriving the PRM term for non-constant properties is as follows. In the typical internal combustion engine system, the constant volume specific heat, c where subscript ‘i’ refers to initial conditions and subscript ‘ref’ refers to the reference conditions. Referring now to The constant volume heat addition is determined as follows. For a constant volume heat addition system, no work is done on the piston. Thus, Eq. (3) becomes 0 because the volume change is 0. Then, the first law of thermodynamics implies that the change in internal energy must equal any heat flowing into or out of the system. For the combustion system considered, the internal energy change only due to combustion needs to subtract the internal energy change due to compression just before heat addition. Heat transfer is neglected because of the short duration of the event. Internal energy is a state variable; therefore, it depends on only starting and ending states. Then, the first law of thermodynamics for this system can be obtained by substituting Eq. (2-7) into Eq. (1), as follows in Eq. (8):
wherein m
Dividing by b×T
Constants k, k2, and B are parameters introduced to simplify the derivation. The constants are defined with Tref assuming specific heat data are stored in a table with values at Tref; optionally a functional definition of the properties with temperature simplifies the expressions with Tref=Ti:
Then, Eq. (10) becomes a simple quadratic equation and Eq. (11) gives the following solutions in Eq. (13).
The temperature ratio is a positive value, giving a final solution as depicted in Eq. (14):
With T For the constant volume heat addition, the ideal gas equation of state is used to relate the temperature ratio to the pressure ratio (PR) as follows:
The temperature ratio is the same as the pressure ratio for a constant volume heat addition. Thus the pressure ratio due to constant volume heat addition in which reactants depend on temperature and combustion charge is as follows:
wherein constants, k, k2, and B, are defined in Eq. (11). The result of Eq. (16) is a pressure ratio between pressure at the end of heat addition and the initial pressure. The pressure ratio is a function of the initial temperature, T The polytropic expansion is determined as follows. It is assumed that the closed system is perfectly insulated, thus, there is no heat transfer. Then, the first law of thermodynamics becomes:
wherein R is the universal gas constant. Rearranging Eq. (17) and applying integration from T
wherein T
Another constant, k3 is defined using Eq. (20). And, dividing Eq. (19) by k3 gives Eq. (21):
Another constant
Knowing that e ^{a}e^{b}=e^{c }and e^{in a}=a, Eq. (22) becomes:
The Taylor series for e
Applying the Taylor series for the second term in Eq. (23) yields:
The second term on the right hand side in Eq. (24) can be neglected. Then, Eq. (23) becomes:
Rearranging Eq. (25) gives a simple quadratic equation as depicted in Eq. (26). Solving this equation gives two solutions, depicted in Eq. (27).
Again, the temperature ratio is a positive value, so rearranging the solution gives the final solution for the temperature ratio for polytropic expansion with variable cylinder charge property. Referring now the bottom portion of
The ideal gas equation of state is used to relate the temperature ratio to the pressure ratio. The pressure ratio for variable properties can be obtained as depicted in Eq. (29). The pressure ratio for constant property is obtained using isentropic expansion, as in Eq. (30).
The ratio of the variable property PR to the constant property PR is as depicted in Eq. (31).
The volume ratios can be combined because the volume ratio is not property dependent. Knowing the ratio of these two PR is convenient because it is apparent how much greater the variable property PR is than the constant property PR. Referring now to the top portion of
For constant property, gamma, i.e., γ, comprises a ratio of specific heats and is nominally chosen as that for air at the temperature corresponding to those used for computing the signal bias and without EGR. Thus, nominally or initially γ=1.365 for diesel engines and nominally γ=1.30 for conventional gasoline engines. These can however be adjusted based on the data from the specific heats for air and stoichiometric products using an estimate of the equivalence ratio and EGR molar fraction targeted for the operating condition and using the relation that [γ=1+(R/cv)] and the weighted average of air and product properties through the expression:
With the expression evaluated at the gas temperature corresponding to that for pressures sampled for the computation of signal bias. The method described hereinabove is readily reduced to be programmed into a microcontroller or other device for execution during ongoing operation of an internal combustion engine, as follows. The trapped mass temperature To, at intake valve closing (IVC) is estimated from predetermined calibrations for the operating condition and the motored temperature, Tmot, using the polytropic expression with the gamma value used as that described, as in Eq. 33:
Using the conventionally computed pressure ratio at measured crank angles (CA) an estimate of the mean gas temperature is computed using the following equation:
Progressively the combustion heat release, i.e., the net heat addition/unit mass, is determined from equation (16) above using the solution of Eq. 16 for B with the property and temperature dependent (k and k2) and the expression in Eq.28 to provide an initial temperature from which the heat of combustion is added. Specifically, T(CAi) of Eq. 34 is used to compute the polytropic expansion temperature with Eq. 28 for the next sample point with Tf=T(CAi) and the solution T, i.e., “Texp”, which is the temperature the gases achieve when expanded from the previous sample without heat addition. The ratio of T(CAi+1) to this computed Texp provides a new PR for the computation of incremental heat addition B(CAi+1), using Eq. 16 with properties evaluated at Texp. The term B reflects the net heat addition which is converted to a mass of fuel burned over the interval using the definitions in Eq. 10 (Ti=Texp) and a correlation of the wall heat transfer as a fraction of the heat release over the interval. This correlation is developed from the base engine calibration. The resulting fuel burned distribution/mass of charge provides the base information to direct the timing of injections as well as appropriately balancing multiple injections. The estimation technique can be applied with increased sample resolution to improve accuracy or be applied with relatively low resolution for less demanding signal processing and convenience for crank angle encoder hardware. The method described herein is applicable for broad ranges of temperature, cylinder charge and timings associated with compression ignition engines, without requiring calibrated pressure sensors. The method is applicable to spark-ignition engines, including those using homogeneous charge compression ignition strategies. The method is applicable to systems utilizing multiple fuel injection events per cylinder event. Referring now to The engine preferably has an air/fuel operating regime that is primarily lean of stoichiometry. The skilled practitioner understands that aspects of the invention are applicable to other engine configurations that operate primarily lean of stoichiometry, e.g., lean-burn spark-ignition engines. During normal operation of the compression-ignition engine, a combustion event occurs during each engine cycle when a fuel charge is injected into the combustion chamber to form, with the intake air, the cylinder charge. The cylinder charge is subsequently combusted by action of compression thereof during the compression stroke. Sensing devices are installed on or near the engine to monitor physical characteristics and generate signals which are correlatable to engine and ambient parameters. The sensing devices include a crankshaft rotation sensor, comprising a crank sensor The actuators are installed on the engine and controlled by the control module The fuel injector The engine may be equipped with a controllable valvetrain operative to adjust openings and closings of intake and exhaust valves of each of the cylinders, including any one or more of valve timing, phasing (i.e., timing relative to crank angle and piston position), and magnitude of lift of valve openings. One exemplary system includes variable cam phasing, which is applicable to compression-ignition engines, spark-ignition engines, and homogeneous-charge compression ignition engines. The control module The control module The control module is adapted to monitor cylinder pressures and engine operating conditions from the aforementioned sensors, preferably and execute program code to determine the combustion phasing and heat release, as previously described. The control module While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims. Patent Citations
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